Process and apparatus for treating wastewater

ABSTRACT

Wastewater can be treated using a combination of a settleable solids separator, such as a vortex separator, and a gas floatation separation system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims priority toU.S. patent application Ser. No. 09/678,229, filed on Oct. 4, 2000 nowU.S. Pat. No. 6,488,853.

TECHNICAL FIELD

This invention relates to a process and apparatus for treatingwastewater.

BACKGROUND

Declining water tables, population growth, increasing industrialization,expanding use of irrigated agriculture, and pollution of fresh watersupplies strain limited fresh water supplies around the world. Reclaimedwastewater can serve as a supplemental source of water, particularly fornon-potable uses. Irrigation of crops and landscaping, which constitutesapproximately 70% of total water demand and which also benefits fromsome of the nutrients present in wastewater, represents one suitablenon-potable use for reclaimed water. Other appropriate non-potableapplications for reclaimed wastewater include washing, cooling, fireprevention and control, creek enhancements, fountains, recreationalponds, cement preparation, dust control, and toilet flushing. Despitethe wide range of non-potable uses, wastewater reclamation typically hasbeen practiced only on a very small scale. Conveyance of reclaimed waterfrom the reclamation site to a site of use and limited productionmethods can represent obstacles to more widespread use of reclaimedwater.

Effective and efficient treatment of wastewater is economically andenvironmentally important. Wastewater treatment systems can includeincineration systems, chemical treatment systems, electrolysis systems,nuclear radiation systems, and physical treatment systems. These varioussystems can provide water of varying quality. Many of theses systems canbe costly and relatively difficult to run and maintain. Physicaltreatment systems such as filtration can be difficult to develop becauseof fouling problems and retarded flow. In addition to chemical andpathogenic impurities, incoming wastewater can include settleablesolids, such as hard and abrasive materials, that can damage componentsof the treatment system and floatable materials, such as fats, oils,greases and fibers that can foul a physical treatment system. Usefulsystems for wastewater treatment can provide consistent output, becapable of automation, be relatively small in size, provide usableliquid and solid byproducts, and be relatively low in cost.

SUMMARY

In general, the invention features a process and apparatus for treatingwastewater streams into beneficial water and solids components using airfloatation separation as a principal treatment. Removal and segregationof materials that adversely affect operation of the air floatationseparator earlier in the treatment process can improve water throughput,water quality and the lifespan of system components. Physical separationof settleable solids and floatable materials from the wastewater priorto treatment with a gas floatation separation system can allow higherflow rates to be achieved.

In one aspect, the invention features a method for treating wastewatercontaining settleable solids to form a reusable liquid fraction. Themethod includes separating a wastewater stream into a first componentand a second component in a first containment zone, and passing thesecond component into a second containment zone including a gasfloatation separation system to form a froth fraction and a reusableliquid fraction. The first component includes an amount of settleablesolids greater than an amount of settleable solids in the secondcomponent. The method can include comminuting the wastewater streamprior to separating the first component and the second component.

Separating can include settling settleable solids by gravity. In certainembodiments, separating can also include settling settleable solids byforces generated by wastewater stream flow into a separation tank.

The method can include introducing bubbles of gas into the secondcomponent in the gas floatation separation system, retaining the secondcomponent in the second containment zone for an interval sufficient toallow the bubbles to rise and pass through the second component to formthe froth fraction, and removing the froth fraction from the secondcontainment zone to leave behind the reusable liquid fraction. Therising bubbles can adsorb suspended particles and dissolved organiccompounds and float them to the surface of the second containment zoneand forming the froth fraction. The method can also include combiningthe first component and the froth fraction to form a slurry stream, and,in certain embodiments, treating the slurry stream. The gas can includeozone.

The reusable liquid fraction can be disinfected. This can beaccomplished by, for example, exposing the reusable liquid fraction toultraviolet radiation. In certain embodiments, disinfecting can includemixing a chemical oxidant, such as ozone, with the reusable liquidfraction.

The reusable liquid fraction can be applied to unsaturated soil. Thesoil can assist in removal and productive reuse of plant nutrientscontained in the reusable liquid fraction, and return purified water tounderlying aquifers.

The method can include passing the reusable liquid fraction through afilter system. The filter system can be backflushed, for example, tocreate a volume of backflushed material and that can be combined withthe slurry stream.

The filter system can include a filter Medium coated with a biofilmwithin a third containment zone. Contact with the biofilm can result inremoval of remaining suspended solids, nitrification of dissolved andsuspended organic nitrogen compounds, and reduction of other sources ofbiochemical oxygen demand.

The wastewater can be obtained from a sewer. The first component and thefroth fraction can be combined to form a slurry stream that can bereturned to the sewer downstream of the location from which thewastewater was obtained. In certain embodiments, the slurry stream canbe passed into a third containment zone to separate it into asupernatant fraction and a settled fraction. Sufficient retention timein the third containment zone can allow for substantial settling ofsettleable solids to the bottom of the zone. In the third containmentzone, solids can be decomposed by a predominately anoxic biologicalprocess. The supernatant fraction can be returned to the firstcontainment zone or the second containment zone, or passed to anunderground leach field.

In another aspect, the invention features an apparatus for treatingwastewater containing settleable solids. The apparatus includes asettleable solids separator and a gas floatation separation system. Thesettleable solids separator includes a vessel having an upper end, alower end, and an outer wall connecting the upper end and the lower end.The settleable solids separator also includes an inlet directedpartially tangentially through the outer wall of the vessel, a firstoutlet proximate to the upper end of the vessel, and a second outletproximate to the lower end of the vessel. The gas floatation separationsystem includes an inlet port and a reusable liquid fraction outletport. The apparatus includes a fluid conduit fluidly connecting thefirst outlet of the settleable solids separator and the inlet port ofthe gas floatation separation system.

The settleable solids separator can be a vortex separator. Thesettleable solids separator can also include a vent and overflow portpositioned between the first outlet and the upper end of the vessel. Thesecond outlet of the settleable solids separator can be a settled solidsoutlet in communication with an opening in the base of the vessel forremoving solids, which are swept towards the opening by a vortex. Thegas floatation separation system can separate and remove remainingsettleable and suspended solids, and certain dissolved solids, in thesupernatant of the settleable solids separator.

The gas floatation separation system can include a gas floatationseparation vessel including an upper end, a lower end, and an outer wallconnecting the upper end and lower end. The inlet port can be proximateto the upper end of the vessel and the reusable liquid fraction outletport can be between the inlet port and the lower end. The vessel canalso include a scum overflow and vent port between the inlet port andthe upper end and a gas injection port between the scum overflow andvent port and the lower end. The gas injection port can be part of aliquid circulation circuit including a port at a low elevation in thegas floatation separation vessel, a pumping inlet conduit, pump, venturinozzle, and a return conduit in communication with the gas injectionport. Liquid circulating through the nozzle draws gas into the stream inthe form of small bubbles, which are introduced into the gas floatationseparator through the gas injection port.

A clarified liquid conduit can fluidly connect the reusable liquidfraction outlet port of the gas floatation separation vessel with adisinfection system, which can include an ultraviolet disinfectionsystem or an ozone treatment system, or both. The ultravioletdisinfection system can include one or more clear plastic tubes that aretransparent to ultraviolet radiation and through which the reusableliquid fraction passes, ultraviolet lamps surrounding the plastic tubes,and an enclosure containing the assembly of tubes and lamps. Theultraviolet lamp apparatus can produce ozone in the air spacesurrounding the lamps. The ozone can be extracted from the enclosure,which can serve as an ozone generator. An ozone transport conduit canfluidly connect a closed atmosphere of the settleable solids separatorand a closed ozone treatment vessel of the ozone treatment system.Exposure to ultraviolet radiation can directly kill organisms, and ifdissolved ozone is contained in the liquid, it can create powerfuloxidizing agents that further disinfect, remove odor and color, reducebiochemical oxygen demand of, and oxidize harmful chemical compounds inthe liquid.

The apparatus can include a wastewater pump, such as a comminutingwastewater pump in fluid communication with the inlet of the settleablesolids separator.

The apparatus can also include a flow restrictor in fluid communicationwith the reusable liquid fraction outlet port of the gas floatationseparation system. The flow restrictor can be used to regulate the flowof the process. Periodically, the flow restrictor can be used to retardflow so as to cause the liquid levels of both the vessel of thesettleable solids separator and the vessel of the gas floatationseparator to rise beyond the overflow ports of both vessels, therebyforcing accumulated scum layer and other floating material on thesurface of the vessels to be discharged to the slurry stream.

In certain embodiments, the apparatus can include a filter system influid communication with the reusable liquid fraction outlet port of thegas floatation separation system. The system can be a backflushablefilter system.

The scum overflow and vent port can be in fluid communication with aslurry fraction conduit. The slurry fraction conduit can be in fluidcommunication with the second outlet of the settleable solids separator.

In particular embodiments, the apparatus can include a solids treatmentsystem. The solids treatment system can include an inlet port and anoutlet port. The inlet port can be in fluid communication with theslurry fraction conduit. The solids treatment system can include avessel with an inlet port in communication with the slurry stream, andan outlet port. The solids treatment system can have a volume sufficientto allow the settleable solids in the slurry stream an opportunity tosettle and decompose by, for example, predominantly anoxic biologicalprocesses. The outlet port of the solids treatment system can be influid communication with the inlet of the settleable solids separator.The outlet port of the solids treatment system can be in fluidcommunication with the inlet of the gas separator vessel or said gasfloatation separation system.

The apparatus can also include a membrane separation system in fluidcommunication with the reusable liquid fraction outlet port.

In another aspect, the invention features a process for reducing odorsin a vessel containing wastewater including introducing ozone into anairspace of the vessel. The ozone can be surplus ozone from an ozonetreatment stage of wastewater treatment. The vessel can be sewer or aportion of a sewer.

The method offers a simple, reliable, rapid, compact and inexpensiveprocess for obtaining reusable water, which can overcome many of thedeficiencies of conventional biological wastewater treatment processes.For example, the apparatus and method performs more reliably andefficiently than paper filter, membrane, or biological systems alone.The apparatus is a complete wastewater reclamation system that, amongother things, can minimize conveyance costs, can avoid the use ofinherently unreliable and maintenance-intensive wastewater treatments,can overcome certain limitations of past physical or chemical systems,can produce reusable or readily disposed residual byproducts, can becompact, economical, reliable, and odorless, and can produce highquality thoroughly disinfected water appropriate to various reuseapplications, such as irrigation and other non-critical reuseapplications, washing, cooling and other industrial uses, or aquacultureand for discharge to surface water bodies. The method an apparatus canalso create an odorless environment in the surrounding of the apparatus.Accordingly, the wastewater reclamation system can be well suited foron-site or local applications in which the water produced is reusedproductively in the vicinity of the treatment plant.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a water reclamation system including asolids treatment system.

FIG. 2 is a schematic view of a water reclamation system including areturn for carrying solid residuals to a sewer.

FIG. 3 is a plan view of a separation tank.

FIG. 4 is a schematic view of filtration and disinfection portions ofthe water reclamation system, the filtration portion being a membraneseparation system.

FIG. 5 is a schematic view of filtration and disinfection portions ofthe water reclamation system, the filtration portion including abackflushable biofilter system.

FIG. 6 is a schematic view of a solids treatment system.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring to FIGS. 1-2, a water reclamation system includes settleablesolids separator 32, such as a vortex separator, gas floatationseparation system 52, such as a foam fractionation tank, filter system78, such as a backflushable filter system, disinfection system 65, andsolids treatment system 92 (FIG. 1) or sewer 20 (FIG. 2). Disinfectionsystem 65 includes ozone treatment system 76 and ultravioletdisinfection system 84. Wastewater 21, which can contain sanitary andother wastes, collects in underground storage tank 22 (FIG. 1) or wetwell 96 (FIG. 2). Underground tank 22 contains submersible sewage pump24. Preferably, pump 24 is a comminuting pump, such as a chopper pumpmanufactured by Vaughan Chopper Pumps of Montesano, Washington, whichsimultaneously chops, or comminutes, larger solids in wastewater 21 intoa slurry. The slurry is pumped via conduit 26, through check valve 28and into settleable solids separator 32 through inlet port 30 ofsettleable solids separator 32.

Settleable solids separator 32 includes vessel 10 having upper end 12connected to lower end 13 by outer wall 14. First outlet 42 is locatedin outer wall 14 near upper end 12. Inlet port 30 is directed partiallytangentially through outer wall 14 near upper end 12. Second outlet 46is proximate to lower end 13. Closed atmosphere 40 of separator 32fluidly communicates with vent and scum overflow port 44 connected tovent and scum overflow conduit 45. Lower end 13 includes second outlet46, which is connected to conduit 49 which includes solids pump 48.Solids pump 48 can be, for example, a progressing cavity pump availablefrom Moyno Inc. of Springfield, Ohio. Referring to FIG. 1, solids pump48 and drain valve 47 empty through conduit 45 into solids treatmentsystem 92, which discharges treated material through output port 94.Referring to FIG. 2, solids pump 48 and drain valve 47 empty throughconduit 45 into sewer 20.

Referring to FIG. 3, inlet 30 of separator 32 is directed to createcentrifugal flow pattern 98 that passes around annular dip plate 34,spillway 36, and the top of baffle 38. Spillway 36 is attached to theinner wall of dip plate 34. First outlet 42 draws fluid from spillway36. Vent and scum overflow port 44 is located to one side of separator32. Second outlet 46 is centered in vessel 10. Annular inner baffle 38,which flares out in a conical shape as it, approaches second outlet 46.

Referring to FIGS. 1-3, first outlet 42 delivers the contents ofspillway 36 to gas floatation separation system 52 via fluid conduit 51.Referring to FIGS. 1-2 and 4-5, gas floatation separation system 52includes vessel 53 that receives output of settleable solids separator32 through inlet port 54. Inlet port 54 is proximate to upper end 55 ofvessel 53. Vessel 53 has reusable liquid fraction outlet port 56 belowinlet port 54 and proximate to lower end 57. Gas injection port 58 ispositioned somewhat above port 56 and proximate to lower end 57, and ascum overflow and vent port 60 toward upper end 55 of vessel 53 drainingto conduit 50. Outer wall 61 connect lower end 57 and upper end 55.

Outlet port 56 is fluidly connected to disinfection system 65. Outletport 56 is part of a circuit feeding back to gas injection port 58through circulation pump 66, conduit 68, gas injector nozzle 70, andconduit 74. Conduit 68 feeds ozone treatment system 69. Gas for thefloatation separation system, such as a mixture of ozone and air fromozone generator 76, feeds injector 70. Sidestream conduit 72 fromconduit 68 conveys a portion of the output from pump 66 through filter78, which can be a backflushable filter, flow control valve 82, andultraviolet disinfection system 84 to output equalization tank 86through inlet port 88. Reusable liquid fraction is discharged fromoutlet 90.

Referring to FIG. 2, residual solids are returned to sewer 20.Wastewater 21 from sewer 20 drains into a wet well 96, which is at anelevation lower than that of sewer 20. Rather than employ a separatesolids treatment system, settled solids from pump 48, foam, gas andfloatable solids from conduits 45 and 50 and filter backflush fromconduit 80 drain back to sewer 20 at points downstream of the entranceto wet well 96.

Referring to FIG. 4, filter system 65 can include membrane separationsystem 100. Suitable membrane separation systems are available fromKomline-Sanderson of Peapack, New Jersey and New Logic International ofEmeryville, California and are described, for example, in U.S. Pat. Nos.6,027,656, 4,952,317, 5,014,564 and 5,837,142, each of which isincorporated herein by reference. A system containing the membraneseparation system can produce water free of particulate materialsprimarily for industrial applications, such as washing and cooling, withreturn of residuals to a sewer. Outlet 56 of gas floatation separationsystem 52 is fluidly connected to pump 66, which outputs to membraneseparation system 100. Bypass valve 108 controls flow to ozone treatmentsystem 69, flow control valve 82 controls flow to membrane separationsystem 100, and drain valve 109 controls flow to sewer 20. Membraneseparation system 100 has both a concentrate output 106 and a permeateoutput 104. Conduits 106 and 110 merge to feed gas injector nozzle 70,which is fluidly connected to gas inlet 58 of vessel 53 through conduit74. Permeate output is fluidly connected through conduit 104 toultraviolet disinfection system 84 and inlet port 88 of outputequalization tank 86. Conduit 104 is also connected to drain valve 105.Drain valves 105 and 109 empty to sewer 20 through conduits 107 and 111,respectively. When necessary, cleaning solution can be supplied to gasfloatation separation system 52 through conduit 113 to tank 52.

In operation of the systems of FIGS. 1-4, wastewater 21 enteringunderground tank 22 or well 96 is pumped via pump 24 through check valve28 into settleable solids separator 32 through port 30, where flow isdirected tangentially to wall 14, thereby causing the contents of theseparator to slowly circulate. Floatable substances, such as fats, oilsand greases, in the wastewater quickly rise along the tank periphery asthe contents of the separator circulate, causing them to become trappedpredominantly in the annular space between dip plate 34 and wall 14.Settleable solids, such as grit, sand, stones, razor blades, plastics,and other foreign solid materials, in the wastewater fall to the bottomof separator 32 by circulating along the outer periphery of theseparator. As the settleable solids reach the bottom of the separator,they are swept inward by centripetal forces created by the differentialvelocities of the circulating fluid on the outside of the baffle and therelatively stationary liquid toward the center. Solids reaching theouter inclined surface of baffle 38 gradually slide downward and outonto the conical bottom surface of the tank. Centripetal forces createdby the relatively quiescent conditions under baffle 38 sweep settledsolids inward and trap them under the baffle. Once trapped inside thebaffle, suspended solids slowly agglomerate and settle to the bottom.The settled solids exit the separator through outlet 46. Liquidrelatively free of settleable and floatable solids and containingprimarily dissolved and suspended solids rises toward the top of theseparator inside of annular dip plate 36, exiting the separator throughspillway 36 and port 42. The component exiting through port 46 containsa greater amount of settleable solids than the component exiting throughport 42.

The fluid component exiting port 42 enters gas floatation separationsystem 52 at inlet 54, where it encounters a continuous rising currentof small gas bubbles 62, such as an air-ozone mixture, injected at port58 that rise in the liquid of separator 52. Bubbles 62 lift solids andfloatable material to liquid surface. The air-ozone bubbles liftsuspended solids, proteins, oils, detergents and other surfactants inthe fluid to the surface and form froth fraction 64 of foam and scum byfoam fractionation. The addition of ozone to the air injected by nozzle70 can assist in disinfection, removal of odor and color, and reductionof chemical oxygen demand in the fluid. The downward flow of liquid frominlet port 54 to outlet 56 opposes the upward flow of the bubbles,increasing the duration and extent of liquid-bubble contact.

A reusable liquid fraction exits outlet 56 in a purified state. Thereusable liquid fraction is substantially free of suspended, settleableand floatable solids, and can be deodorized, disinfected, and colorfree. Under pressure from pump 66, a portion of the reusable fraction isdiverted by conduit 72 to pass through backflushable filter system 78that traps any larger suspended solids that might remain. The filtratefrom filter system 78 passes through flow control valve 82, and thenthrough ultraviolet disinfection system 84, which kills organisms in thereusable liquid fraction that might still be viable by imparting directgermicidal radiation. Ultraviolet radiation from system 84 also destroysresidual ozone in the reusable fraction by, for example, convertingdissolved ozone into hydrogen peroxide and highly reactive free radicalsthat further disinfect the water, remove color and odor, and oxidizeundesirable substances. Backflush from filter 78 is conveyed to solidstreatment system 92 by conduit 80, where it joins settled and floatablesolids, and foam and gases from the prior treatment stages.

Several types of filter systems can be selected for filter system 78.One preferred system is a backflushable filter system that uses aplurality of disk filters, such as the disk filtration systemsmanufactured by Arkal Filtration Systems of Kibbutz Bet Zera, JordanValley, Israel, which are capable of filtering out materials as small as10 microns, provide continuous flow using a plurality of filter modules.Suitable filter systems are described in U.S. Pat. No. 4,655,911, whichis incorporated herein by reference. In the system depicted in FIG. 1, afilter porosity of 20 microns or less is desirable to remove particulatematerials of concern. The backflushable filter system can use a simpleand reliable backflush method that backflushes one filter module at atime, while the modules not being backflushed continue to be availableto filter water. An air-assisted backflushing step can produce a lowvolume of backflush, which can decrease the backflush output of thesystem. The backflushable filter system can employ an automaticbackflush cycle that is triggered when the pressure differential acrossthe component filters exceeds a predetermined value.

The settling of solids and gas floatation separation that precede abackflushable filter system remove a large fraction of settleable,floating and suspended solids in the wastewater, thereby minimizing theworkload for the filter and correspondingly, the duration and frequencyof backflushing that is needed. Also, when ozone is used in the gasfloatation separation system, biological growth in filter system 78 canbe reduced or eliminated.

Flow control valve 82, sewage pump 24, circulation pump 66, and settledsolids pump 48, work in a coordinated manner to control the overallsystem. When operation is first initiated, pump 66 is operated to chargegas floatation separation system 52 with air and ozone, therebypurifying water in vessel 53, while pump 24 remains turned off and valve82 is closed to block any output. After an interval sufficient to cleanthe water at the bottom of vessel 53, sewage pump 24 is started andvalve 82 is opened. Flow rates are set to maintain a desired flow ratethrough the system. Under ordinary operating conditions, valve 82typically is set to match the flow into the system through pump 24 sothat the liquid levels in vessels 10 and 53 remain stable. One way tocontrol flow through valve 82 is by interconnecting it with a floatpilot valve in vessel 53, such as is provided by the Bermad model 700-60float-controlled valve system available from Bermad Control Valves ofAnaheim, California.

During operation of the system, scum layers will develop on the surfacesof the liquid in both vessels 10 and 53. Scum layers can be purged fromthe system by periodically closing valve 82 for an interval whileleaving input pump 24 running. This causes the liquid levels in bothvessels 10 and 53 to rise, and eventually spill over through ports 44and 60 through conduits 45 and 50 into solids treatment system 92(FIG. 1) or sewer 20 (FIG. 2). Once the scum layers have been purged,valve 82 can be opened again to modulate flow by valve 82 to return theliquid level in tank 52 to the target level.

Settled solids pump 48 is turned on and off periodically in coordinationwith the total flow through the system to meter out controlled amountsof solids residuals to solids treatment system 92 (FIG. 1) or sewer 20(FIG. 2). For the embodiment of FIG. 1, the solids are concentrated to ahigh degree prior to treatment, in the range of 5% solids by weight, tominimize the volumes in need of subsequent treatment. The higher solidscontents can be achieved by metering the solids residuals using pump 48.Normally drain valve 47 is closed, but it can be opened to drain tank 32quickly.

Settleable solids separator 32 and gas floatation separation system 52both can have closed atmospheres. This prevents release of odorous gasesto the environment surrounding the system. Additional odor control canbe provided by surplus ozone released under pressure to airspace 41 ofvessel 53 from the rising injected bubbles 62 in the tank. This ozonecan also permeate airspace 40 of vessel 10, as well as interconnectingconduits and solids treatment system 92. This ozone-containingatmosphere can further reduce odors by, for example, oxidizing H₂S,mercaptans, and other malodorous or harmful gases in the airspaces.Chemical reactions with the ozone not only deodorize and destroy thesematerials, but also consumes excess ozone.

The reusable liquid fraction generated by the system can besubstantially clear, odorless, colorless, disinfected, and free ofsuspended solids. The reusable water recovered using the system depictedin FIG. 1 can have beneficial attributes for irrigation use. Forexample, the water can contain organic forms of desirable plantnutrients, including trace minerals and nitrogen in organic forms suchas urea, which can then be captured by soil particles and convertedslowly into nitrates usable by plants. In addition, the reusable watercan contain detergents, which can render heavy clay soils more porous,and hydrogen peroxide created by ozone injection, which can improve thehealth and activity of plant roots.

The treatment process can be relatively rapid. The size of the systemcan be determined, in part, by the dimensions of vessels 10 and 53,which can be taller than they are wide, and have relatively smallvolume. Typical water retention times are approximately 15 minutes invessel 10, and 10 minutes in vessel 53. In comparison, biologicaltreatment systems can have hydraulic retention times between 4 hours andseveral days. Wastewater can be treated in approximately 30 minutes insurface tanks, which can preserve the heat value of the wastewater,which can be supplemented by the pumping energy added by the equipment.Since municipal wastewater typically has a temperature of 65-70° F., theheat can be released in greenhouses during cold months. In addition,because the systems of FIGS. 1-2 and 4 use physical separation methods,intermittent use of the system can be facilitated, for example, whenthere is need for the water. Systems that use biological purificationmethods can require more stable operating conditions than physicalsystems.

The system depicted in FIG. 2 can be compact, having a very smallfootprint, rendering it very practical for potential deployment indeveloped areas where land is scarce and land prices are high. Inaddition, because the solids are returned to the sewer, there is adecreased need to concentrate solids to a high degree Accordingly, pump48 can be operated with a higher duty cycle than in the system of FIG.1.

The compact nature of the system, and the low odor and noise emissionsof the system, allow it to be sited close to populated areas. As long asthere are sewers nearby, the system can be sited near a location wherethe,recycled water is needed, such as, for example, in an urban park ora golf course. The attributes of the system allow lower cost and morepractical wastewater reclamation to be achieved.

Referring to FIG. 4, the system can be operated by first opening valve108 for a period of time to allow gas, such as air and ozone, to fillvessel 53, thereby purifying the water exiting port 56. Valves 82 and109 can be closed at this point, blocking any output from the system.After an interval to assure that water is purified sufficiently, valve108 can be closed and valve 82 can be opened to regulate flow to matchthat of the input pump, as described above. Subsequently, all flowfollows the circuit through membrane separation system 100, with asidestream exiting the system as permeate through conduit 104 andpassing through ultraviolet disinfection system 84. Over time, suspendedand dissolved solids in vessel 53 can become increasingly concentrated,which can foul the membrane of system 100. Fouling of the membrane canresult in higher feed pressure when the permeate flow rate ismaintained. When higher pressures are detected by an external controlsystem, a cleaning cycle can be initiated after a predetermined pressurethreshold is reached. During the cleaning cycle, the following sequencecan be followed: (1) flow to vessel 53 through inlet port 54 is stoppedby shutting off pump 24; (2) vessel 53 is purged by opening drain valve109, and closing valves 108 and 82; (3) vessel 53 is filled with acleaning solution, such as, for example, a combination of hot water andlye through input 113; (4) valve 82 and 105 are opened; (5) the cleaningsolution is circulated for a period of time through membrane separationsystem 100, with a fraction thereof exiting as permeate through valve105 back to sewer 20; and (6) valve 82 is closed and valve 109 isopened, causing the cleaning solution to be pumped out of tank 52through valve 109, conduit 111 and into sewer 20. Following the cleaningcycle, the startup sequence can be initiated by opening valve 108,closing valves 105 and 109, and turning on pump 24 to cause new fluid tobe admitted to tank 52 through inlet 54.

The separating characteristics of membrane separation system 100 can beused more efficiently because most of the settled, floating, andsuspended solids of the wastewater have been removed by settleablesolids separator 32 and gas floatation separation system 52. Inaddition, the introduction of ozone into the flowstream prior tomembrane separation can decrease the formation of biological growthsthat can occur in system 100, and can adversely affect its efficiency.

Referring to FIG. 5, filter system 65 can include backflushablebiofilter system 112 as the filter element in combination withultraviolet disinfection system 84. When biofilter system 112 ispresent, the reusable liquid fraction can be used in applications suchas aquaculture or discharge to surface water bodies where it can beimportant that the nitrogen compounds in the water be nitrified and havea low biochemical oxygen demand. For aquaculture use, the rapidtreatment process can preserve heat in the water. In general, filter 78is replaced by backflushable biofilter system 112. Only air is admittedto the flowstream of conduit 74 through injector nozzle 70, since ozonecan destroy the biofilm on the biofilter medium. Air provides the gasfor floatation separation in system 52 and drives out malodorous gases,and furthermore, provides oxygen needed by the aerobic organisms of thebiofilter. The biofilter system typically is not compatible with ozone.Suitable backflushable biofilter systems are described in U.S. Pat. Nos.5,232,586 and 5,445,740, where are incorporated herein by reference, andinclude the Bubble Washed Bead Filters and Propeller Washed Bead Filtersmanufactured by Aquaculture Systems Technologies L.L.C. of Jefferson,La. Since ozone is not injected into the flowstream, disinfection isprovided by ultraviolet disinfection system 84. Backflushing ofbiofilter systems can be accomplished using gravity with compressed airor a motorized propeller to agitate the filter medium and to loosenaccumulated material. The frequency of backflushing for the biofiltersystem can be carried out at a regular operational interval, or can betriggered by an increase in feed backpressure.

Referring to FIG. 6, solids treatment system 92 includes undergroundtank 114, which can resemble a septic tank for treatment of residentialwastewater. Tank 114 has an inlet port 116, baffle 118 and conduit 120between two containment zones of the tank, and outlet port 122. Inletport 116 receives by gravity settled solids, gases, foam, and floatablesolids collected in other parts of the system from conduits 45 and 50and the filter backflush of 30 conduit 80. Output of tank 114 isconveyed through port 122 back to tank 22.

Operation of solids treatment system 94 can be similar to that of aseptic tank. The system can operate as an unheated, unmixed anaerobicdigester. By design, solids concentrations of the influent can be up to50 to 100 times greater than that in a typical septic tank for a singlefamily home. As a result, the retention times in the tank can beincreased to allow suspended solids considerable time to agglomerate andsettle. If, for example, a typical single family septic tank of 1000gallons retention were used to treat the sewage of 20 homes, theretention time would be approximately 8 to 16 days. The liquid of tank114 in the clear space between the settled and scum layers can bereturned to tank 22 of the system rather than to a leach field. Suchliquid will already have undergone partial decomposition by bothfacultative and anoxic processes. The fate of certain dissolvedmaterials remaining in the liquid returned from tank 114 to tank 22 willdiffer depending on the type of filtration used in the system aresummarized in Table 1.

TABLE 1 Fate with Other Type of Dissolved Material Fate with BiofilterTypes of Filters Ammonia, urea and other Nitrified to Passed on tooutput organic nitrogen compounds nitrate forms unchanged CarbohydratesOxidized to H₂O Passed on to output and CO₂ unchanged

Ozone gas from airspace 41 of vessel 53 can enter the airspace of solidstreatment system 92 to destroy H₂S, CH₄ and odors. As with aconventional septic tank, grit and other inert residual solids in thetank can be removed and disposed periodically, such as by pump truck.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, although Municipal and sanitary wastewater can serve aspredominant sources of wastewater, other sources are also suitable,including fish tanks and ponds, livestock feedlots, food processingplants, lakes, rivers and streams. In addition, reverse osmosis can beused as a post treatment to the membrane separation system if water ofthe highest purity is desired. Furthermore, a solids treatment systemcan be used in conjunction with a membrane separation system. Inembodiments, ozone injection can be used as a supplementary treatmentfor the effluent from a biofilter system or a grinder assembly can beused with the settled solids pump. Moreover, other solids treatmentsystems, such as a heated and mixed anaerobic digester or an autothermalthermophillic anaerobic digester (ATAD) can be used.

What is claimed is:
 1. An apparatus for treating wastewater containingsettleable solids comprising: a settleable solids separator comprising:a vessel having an upper end, a lower end, and an outer wall connectingthe upper end and the lower end; an inlet directed partiallytangentially through the outer wall of the vessel; a first outletproximate to the upper end of the vessel; and a second outlet proximateto the lower end of the vessel; a gas floatation separation systemhaving an inlet port and a reusable liquid fraction outlet port; and afluid conduit fluidly connecting the first outlet of the settleablesolids separator and the inlet port of the gas floatation separationsystem.
 2. The apparatus of claim 1, wherein the settleable solidsseparator is a vortex separator.
 3. The apparatus of claim 1, whereinthe settleable solids separator further comprises a vent and overflowport positioned between the first outlet and the upper end of thevessel.
 4. The apparatus of claim 1, wherein gas floatation separationsystem comprises: a gas floatation separation vessel comprising an upperend, a lower end, and an outer wall connecting the upper end and lowerend, wherein the inlet port is proximate to the upper end of the vesseland the reusable liquid fraction outlet port is between the inlet portand the lower end, the vessel further comprising: a scum overflow andvent port between the inlet port and the upper end; and a gas injectionport between the scum overflow and vent port and the lower end.
 5. Theapparatus of claim 4, wherein the scum overflow and vent port is influid communication with a slurry fraction conduit, the slurry fractionconduit being in fluid communication with the second outlet of thesettleable solids separator.
 6. The apparatus of claim 5, furthercomprising a solids treatment system comprising an inlet port and anoutlet port, the inlet port being in fluid communication with the slurryfraction conduit.
 7. The apparatus of claim 6, wherein the outlet portof the solids treatment system is in fluid communication with the inletof the settleable solids separator.
 8. The apparatus of claim 6, whereinthe outlet port of the solids treatment system is in fluid communicationwith the inlet of the, gas separator vessel or said gas floatationseparation system.
 9. The apparatus of claim 1, further comprising aclarified liquid conduit fluidly connecting the reusable liquid fractionoutlet port of the gas floatation separation vessel with a disinfectionsystem.
 10. The apparatus of claim 9, wherein the disinfection systemincludes an ultraviolet disinfection system.
 11. The apparatus of claim10, wherein the disinfection system further includes an ozone treatmentsystem.
 12. The apparatus of claim 10, wherein the disinfection systemincludes an ozone treatment system.
 13. The apparatus of claim 12,further comprising an ozone transport conduit fluidly connecting aclosed atmosphere of the settleable solids separator and a closed ozonetreatment vessel of the ozone treatment system.
 14. The apparatus ofclaim 1, further comprising a wastewater pump in fluid communicationwith the inlet of the settleable solids separator.
 15. The apparatus ofclaim 14, wherein the wastewater pump is a comminuting wastewater pump.16. The apparatus of claim 1, further comprising a flow restrictor influid communication with the reusable liquid fraction outlet port of thegas floatation separation system.
 17. The apparatus of claim 1, furthercomprising a filter system in fluid communication with the reusableliquid fraction outlet port of the gas floatation separation system. 18.The apparatus of claim 17, wherein the filter system is a backflushablefilter system.
 19. The apparatus of claim 1, further comprising amembrane separation system in fluid communication with the reusableliquid fraction outlet port.